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Hydrus
Hydrus is a small constellation in the deep southern sky. It was first depicted on a celestial atlas by Johann Bayer in his 1603 ''Uranometria''. The French explorer and astronomer Nicolas Louis de Lacaille charted the brighter stars and gave their Bayer designations in 1756. Its name means "male water snake", as opposed to Hydra, a much larger constellation that represents a female water snake. It remains below the horizon for most Northern Hemisphere observers.
The brightest star is the 2.8-magnitude Beta Hydri, also the closest reasonably bright star to the south celestial pole. Pulsating between magnitude 3.26 and 3.33, Gamma Hydri is a variable red giant some 60 times the diameter of our Sun. Lying near it is VW Hydri, one of the brightest dwarf novae in the heavens. Four star systems have been found to have exoplanets to date, most notably HD 10180, which could bear up to nine planetary companions.
==History==
Hydrus was one of the twelve constellations established by the Dutch astronomer Petrus Plancius from the observations of the southern sky by the Dutch explorers Pieter Dirkszoon Keyser and Frederick de Houtman, who had sailed on the first Dutch trading expedition, known as the ''Eerste Schipvaart'', to the East Indies. It first appeared on a 35-cm (14 in) diameter celestial globe published in 1598 in Amsterdam by Plancius with Jodocus Hondius. The first depiction of this constellation in a celestial atlas was in the German cartographer Johann Bayer's ''Uranometria'' of 1603.〔(【引用サイトリンク】Hydrus (Water Snake) )〕 De Houtman included it in his southern star catalogue the same year under the Dutch name ''De Waterslang'', "The Water Snake", it representing a type of snake encountered on the expedition rather than a mythical creature. The French explorer and astronomer Nicolas Louis de Lacaille called it ''l’Hydre Mâle'' on the 1756 version of his planisphere of the southern skies, distinguishing it from the feminine Hydra. The French name was retained by Jean Fortin in 1776 for his ''Atlas Céleste'', while Lacaille Latinised the name to Hydrus for his revised ''Coelum Australe Stelliferum'' in 1763.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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